Biaxially stretched, blow molded bottles made of polyethylene terephthalate (hereinafter abbreviated as PET) are in use in various fields, such as beverages, foods, cosmetics, and the like. In the use applications especially requiring a gas barrier property, the bottles to be used are made by laminating an intermediate layer comprising a gas barrier resin, such as a nylon resin, an ethylene-vinyl alcohol copolymer, etc., with substrate layers made of a PET resin, i.e., the main resin, in a manner embedded therein. Patent document D1 describes a biaxially stretched, blow molded bottle, in which an intermediate layer made of a nylon resin is laminated with substrate layers made of a PET resin, and a process for molding a laminated preform in a test tube shape, which is a primary molded product used to mold the bottle.
In these biaxially stretched, blow molded bottles having an intermediate layer made of a gas barrier resin, such as a nylon resin, etc., laminated with, and embedded in, the substrate layers made of a PET resin, the substrate layers of the PET resin are in tight contact with the intermediate layer of the gas barrier resin, but in many cases, these two types of layers are not adhered to each other. There might be a fear that both types of layers are partially delaminated by an action of shearing force as caused by, e.g., an impact of fall. And once there occurs partial delamination, such as described above, in the bottle for use in, for example, carbonated drinks, carbon dioxide gas permeates the inner layer of the PET resin, and goes into a space between the inner layer and the intermediate layer of the gas barrier resin. The pressure of carbon dioxide cause by the intrusion allows the delamination to proceed further. At some point, the delamination would become visible from outside because of light scattering or reflection on the delaminated interface and result in a problem of damaged appearance, which in turn, causes customers to have a concern for quality.
In this regard, the patent document D2 filed by the applicant of the present application describes an invention of a laminated bottle that has been made to solve the problem of delamination in the bottles having an intermediate layer, such as described above. FIGS. 11 and 12 show an example of the bottle described in the patent document D2. This bottle 601 has a neck 602, a neck ring 603, a shoulder 604, a body 605, and a bottom 606. As shown in a plane cross-sectional view of FIG. 12, the body wall in a height rage h2 has a laminar structure, in which an intermediate layer 613 made of a nylon resin is sandwiched between an outer layer 611a and an inner layer 611b, both of which are substrate layers 611 made of a PET resin. This bottle 601 is characterized in that the intermediate layer 613 is segmented into 16 strips in this embodiment in a circumferential direction by vertical connecting zones 614, where the outer layer 611a is connected directly with the inner layer 611b to form these vertical zones having no intermediate layer.
Even if any impact of fall causes the delamination to take place in this bottle 601 in one of the strips circumferentially segmented by the vertical connecting zones 614, the delamination can be prevented from occurring in adjacent strips by these vertical connecting zones 614. Since the delamination is limited locally, it is possible for the bottle to maintain good appearance in a transparent state.
FIGS. 13(a) and 13(b) show an embodiment of the preform in the shape of a test tube, to be used to biaxially stretch and blow mold the above-described bottle 601, in which FIG. 13(a) is a front view; and FIG. 13(b), a plane cross-sectional view taken along line D-D in FIG. 13(a). Like the bottle 601, this preform 501 has a laminar structure in which an intermediate layer 513 made of a nylon resin is laminated with substrate layers 511 made of a PET resin and is segmented by the 16 vertical connecting zones 514 disposed in parallel in a circumferential direction.
This preform 501 is molded by utilizing an injection molding device having a nozzle section, in which flow channels are disposed to allow the nylon resin to be formed into the intermediate layer 513 and to laminate it with the substrate layers made of the PET resin. Sixteen vertical blocking rib pieces are disposed in the circumferential direction with equal central angle intervals at an end on the downstream side of a cylindrical middle channel through which the nylon resin flows. These rib pieces inside the nozzle section segment the flow of the nylon resin into small streams in the circumferential direction to form 16 vertical connecting zones 514 in the body of the preform 501.